1. Field of the Invention
The present invention relates to a vertical alignment liquid crystal display device which is driven by multiplex driving.
2. Description of the Background Art
A liquid crystal display device is broadly used as an information display unit in various electronic devices for consumer or automobile use. In General, a liquid crystal display device is configured by disposing a liquid crystal layer made of a liquid crystal material between two substrates that are placed opposite each other with a gap of roughly several micrometers. As one type of this kind of liquid crystal display device, a vertical alignment liquid crystal display device is known (For example, refer to Japanese Unexamined Patent Application publication No. 2005-234254). A vertical alignment liquid crystal display device comprises, as its main components, liquid crystal cells of a VA mode in which liquid crystal molecules are aligned substantially vertically relative to the surface of the respective substrates within the liquid crystal layer that are disposed between the two substrates, and polarizers that are respectively provided to the outside of the liquid crystal cells. The respective polarizers are often provided in a crossed Nicol arrangement. Based on the foregoing arrangement, since the transmittance of the liquid crystal display device during the non-application of voltage will be extremely low, it is possible to realize a high contrast relatively easily.
When realizing image display by a liquid crystal display device based on multiplex driving, for instance, substrates respectively having a striped-shaped electrode are placed opposite each other so that the extending directions of the respective electrodes become substantially orthogonal, and the regions where the electrode of one substrate and the electrode of the other substrate intersect become the pixel, respectively. Here, the shape of the respective pixels is substantially rectangular. Moreover, alignment treatment such as rubbing treatment is performed on the surface of the respective substrates. The direction of the alignment treatment to be performed on the surface of the respective substrates is set, for example, in opposite directions (anti-parallel alignment). Consequently, the alignment direction of the liquid crystal molecules during the non-application of voltage settles into one direction at the substantial center in the layer thickness direction of the liquid crystal layer provided between the substrates. For example, when the direction of the alignment treatment to the respective substrates is set to the 6 o'clock direction and the 12 o'clock direction when viewed from the front of the liquid crystal display device, the alignment direction of the liquid crystal molecules settles into the 6 o'clock direction at the substantial center of the liquid crystal layer. Here, the extending direction of the electrode of one substrate becomes substantially parallel to the alignment direction of the liquid crystal layer at the substantial center of the liquid crystal layer, and the extending direction of the electrode of the other substrate becomes substantially orthogonal.
In the foregoing vertical alignment liquid crystal display device, considered is a case of disposing a pair of polarizers, which is provided in a substantial crossed Nicol arrangement, on the outside of the respective substrates. With one of the polarizers, let it be assumed that its absorption axis is disposed at an angle of substantially 45° (degrees) relative to the direction of the alignment treatment that was performed to one substrate. When the liquid crystal layer is formed using a liquid crystal material having a negative dielectric constant anisotropy, and a voltage that is not less than a threshold voltage is applied between the electrodes of the respective substrates, most of the liquid crystal molecules in the liquid crystal layer become inclined in the horizontal alignment direction according to the direction of the alignment treatment. On observing this liquid crystal display device, a light display state is favorably observed from the 6 o'clock direction, and, contrarily, a light display state is not observed from the 12 o'clock direction. The 6 o'clock direction in the foregoing case is referred to as the optimal viewing direction (optimal viewing orientation), and the 12 o'clock direction is referred to as the anti-viewing direction (anti-viewing orientation).
In the foregoing vertical alignment liquid crystal display device, on observing the liquid crystal display device from the anti-viewing direction in a state where the liquid crystal display device is in a light display state when viewed from the front, a substantially dark state can be observed within the pixels, but light leakage occurs in the vicinity of one edge among the four pixel edges of the rectangular pixel. This light leakage occurs without regularity and differs in the respective pixels, and considerably drops the display quality from the appearance.
Moreover, in the foregoing vertical alignment liquid crystal display device, there are cases where a dark region appears in the respective pixels in a state where the liquid crystal display device is in a light display state when viewed from the front during multiplex driving, causing the display quality to drop. Since this phenomenon becomes more notable when the frame frequency is reduced, it is necessary to set the driving frequency higher in order to eliminate this phenomenon. Nevertheless, if the driving frequency is increased, the impedance between the electrodes will also increase, which causes the consumption current to increase and the load of the drive unit to increase, the potential difference of the electrodes will also become obvious, and cause the display quality to drop. Specifically, so-called crosstalk is more easily generated.